Microscopic anatomy and ultrastructure of a Polian vessel in the sipunculan Thysanocardia nigra Ikeda, 1904 from the Sea of Japan

Abstract

The microscopic anatomy and ultrastructure of a Polian vessel have been studied in the sipunculan Thysanocardia nigra Ikeda, 1904 from the Sea of Japan using the methods of histology and electron microscopy. We describe ultrastructural features of the inner and outer coelothelium, which is constructed of podocytes and multiciliary cells. Between the processes of the podocyte cells, we found double diaphragms that are considered characteristic macromolecular filters. We conclude from an analysis of the ultrastructural features of the vessel wall that coelomic fluid may be filtered from the tentacular coelom to the trunk coelom via the wall of the Polian vessel.